What will Hurricane Florence mean for the Washington area?

Washington is waterlogged, and the last thing it needs is a hurricane deluge and damaging winds. Unfortunately, this will be a possibility Friday and into the weekend. But there are scenarios in which we would avoid serious effects.

Flooding rain and winds strong enough to bring down trees are the biggest concerns. But other storm hazards could affect the region, as well.

Depending on the track of Category 4 Hurricane Florence, a storm surge could come up the tidal Potomac and Chesapeake like a bulldozer, pushing water multiple feet above normally dry land along their shores.

In addition, quick-hitting tornadoes could form in some of the storm bands that pass through the region.

"The potential for a disaster is high,” said Jim Lee, meteorologist in charge at the National Weather Service serving the Washington area. But he stressed uncertainties in the specific outcomes, noting that storm effects are still several days away. “Time will tell as the week unfolds."

Seven-day rainfall forecast from the National Weather Service. It predicts 3 to 5 inches of rainfall in the general area over the next seven days but much larger amounts to the southwest, where confidence is higher that excessive amounts of heavy rain will occur. (Capital Weather Gang)

We are very vulnerable

Our soils are saturated and our rivers, creeks and streams are full, if not already overflowing. If we receive several inches of rain or more, flooding will be inevitable, and it could become severe in a worst-case scenario.

"Certainly we're primed," Lee said of any flooding. “Even if we're on the northern fringe [of the storm], we're going to have flooding issues. We're sitting on a powder keg."

As of late August, Washington had already received a year's worth of rain, about 40 inches. Since then, we've picked up another half a foot. The 45.86 inches of rain so far this calendar year ranks it as the fourth-wettest in records that date to 1872.

Storm scenarios

In this scenario, the storm would make landfall between northern South Carolina and the North Carolina Outer Banks and move northwest through central North Carolina into southwest or south-central Virginia, where it would slow or stall.

In the Washington region, there would be a sharp gradient between more-moderate rains to our north and northwest and extremely heavy rainfall to our southwest and south that could continue for days — even into early next week.

European-model rainfall forecast Saturday through Tuesday.

Serious, possibly disastrous flooding would occur in central Virginia and could spill into the central and northern Shenandoah Valley and north-central Virginia piedmont.

The immediate Washington region would receive several inches of rain, certainly enough to cause flooding but perhaps short of widespread, severe flooding.

In this scenario, the storm would make landfall between northern South Carolina and the North Carolina Outer Banks, and progress north through eastern North Carolina and east-central Virginia along the Interstate 95 corridor. It would eventually pass through Northern Virginia west of I-95.

In this scenario, the Washington region generally dodges the bullet as the heaviest rain and strong winds remain well south of the region. Some rain and gusty winds could still skirt the area, especially on the south side, and cause pockets of flooding and a few downed trees, similar to the rain and wind this past weekend.

The American (GFS) model keeps Florence's storm center near the Outer Banks of North Carolina and never brings it far enough north or west to bring significant wind and rain to the Washington area.

The American model (both the new and old) favors this kind of scenario.

Scenario 4: Other (15 percent)

As or just after Florence makes landfall, steering currents will become weak, which turns its future motion into a bit of a wild card. While we have outlined above what we think are the most likely scenarios, there's still the possibility it just meanders near the coastline or edges north or south of current expectations.

We're still four to five days, at least, from any direct effects from this storm, and we will try to reduce the number of scenarios and provide more specifics about what to expect as time wears on.

Preparation

While there is a great deal of uncertainty with respect to the specific effects from the storm in our region, now is certainly the time to begin thinking about preparation for this storm. Prepare for flooding by decluttering drains and gutters. If you have a basement that floods, think about moving any valuables to higher ground.

Do you have trees that could fall on your house during a windstorm? Trim them now.

Jason SamenowJason Samenow is The Washington Post’s weather editor and Capital Weather Gang's chief meteorologist. He earned a master's degree in atmospheric science and spent 10 years as a climate change science analyst for the U.S. government. He holds the Digital Seal of Approval from the National Weather Association. Follow